Considering that the story ostensibly takes place in the Sengoku, it's odd a poor farming village even have white rice to begin with. Rice-milling was a very labour and time-consuming process, and it wasn't until the spread of the waterwheel in the high Edo that polished rice became more widespread in the cities. Edo didn't get its first rice milling shops until the 1650s.

The film perhaps has an excuse that the village has a waterwheel. Note that even then, we probably wouldn't consider their white rice white by our standards. Consensus is that city commoners ate 70% milled rice. The highest polished rice was 3.5 percent more expensive than the least polished (but still polished) rice in the mid-19th century Edo, and a lot of the most polished rice was used to brew alcohol.

And even then, it was unlikely for a farming village (and a really poor one at that) to have ate white rice:

Only high-ranking people within the elite class ate white rice [during the Edo period]. While culture advanced rapidly during the Genroku era [1688-1703], everyone outside of Edo, Kyoto, or Osaka was eating unpolished brown rice.

Even in the early 20th century:

Not only was the average peasant family's diet nutritionally lacking, it was also dull and monotonus. Peasant girls recruited for work in textile factories, or even in brothels, were often ensnared simply by the prospect of being able to eat better than they did at home. A textile worker from a village in Kyushu, who worked in Osaka in the 1930s, recalled, "What pleased me most was the fact that I could eat all I wanted. At home I used to eat a pasty mixture of yam and chestnut, and instead of white rice, we had brown rice mixed with barley....At home we got fish no more than once a year, on New Year's."

And the famous poem by Kenji Miyazawa:

一日ニ玄米四合ト
味噌ト少シノ野菜ヲタベ
Dining daily on four cups of brown rice
Some miso and a few vegetables

Most peasants in the Sengoku and Edo would probably have ate some type of grain other than rice, and ate brown rice when they did have rice. You can read more about the diet of early modern Japanese peasants here by /u/wotan_weevil and I. Did they consider the diet bland? Yes (see quote above). But the alternative was starvation.

Now if the village actually also grew a bunch of other mixed grains and vegetables, and gave the (brown) rice to the samurai while the peasants ate the mixed grains, that would've been more accurate. But I guess explaining 16th-17th century farming would take away from the pacing of the story.